Two invar boilers should be consuming 24 hu/t if I remember, I think invar outputs 48 steam/t? so say 96 steam/t to a bronze engine, bronze engine should push 48 ku/t same as the dense boiler setup.
Correct me if I’m wrong I’m writing from memory just now.
so at that 3 invar boilers should be 144 steam/t reaching 72 ku/t that would overshoot the bronze steam engine limit of 64 ku/t I think, right? Was your piping longer yesterday or something.
Also I might be off on my figures somewhere.
EDIT
oh use a magnifying glass to check steam pressure at different pipes, see if there is a difference.